1. Field
An aspect of the present invention relates to a thin film transistor (TFT) using an oxide semiconductor as an active layer, a method of manufacturing the TFT and an organic light emitting display device having the TFT. More particularly, an aspect of the present invention relates to a TFT having two gate electrodes disposed into a non-symmetric structure, a method of manufacturing the TFT and an organic light emitting display device having the TFT.
2. Description of the Related Art
In general, a thin film transistor (TFT) includes an active layer and a gate electrode. Here, the active layer provides channel, source and drain regions. The gate electrode overlaps with the channel region and is isolated from the active layer by a gate insulating layer.
The active layer of the TFT configured as described above is usually formed of a semiconductor such as amorphous silicon or poly-silicon. However, if the active layer is formed of amorphous silicon, mobility is low, and therefore, it is difficult to implement a drive circuit operated at a high speed. If the active layer is formed of poly-silicon, the mobility is high, but threshold voltage is uneven. Therefore, a separate compensating circuit is necessarily added.
In a related art method of manufacturing a TFT using a low temperature poly-silicon (LTPS), a high-priced process such as laser heat treatment is performed, and it is difficult to control characteristics of the TFT. Therefore, it is difficult to apply the related art method to large-area substrates.
To solve such and/or other problems, studies have recently been conducted to develop a TFT using an oxide semiconductor as an active layer.
Japanese Laid-Open Patent Application No. 2004-273614 discloses a TFT in which a zinc oxide (ZnO) or an oxide semiconductor using the ZnO as a main element is used as an active layer.
The oxide semiconductor using the ZnO as a main element is a material that is amorphous and stable. Such an oxide semiconductor is used as an active layer, so that a TFT can be manufactured at a low temperature using existing processing equipment without the need of additional separate processing equipment, so that an ion implanting process can be omitted, and the like.
However, the unit resistance of the oxide semiconductor is higher than that of the poly-silicon. Therefore, the structure of the related art TFT has difficulty implementing electrical characteristics necessary for a pixel drive circuit of a display device or a peripheral circuit.